The present invention relates to flexible liners for septic tanks, especially in a retrofit application. It is an object of the present invention to provide apparatus designed to facilitate the production of hollow cast articles such as septic tanks and concrete vaults, to facilitate separation between a carting and the forms used in making the casting, and to expedite the entire casting operation.
The prior art is filled with references to flexible tank liners and adaptations to fill and drain conduits, as well as upper and side support devices for the sidewalls. One example of a drain tank liner is shown in U.S. Pat. No. 5,656,766. A flexible liner forms a gas tight seal about the walls of an underground concrete vault. A concrete lid pressing on a circumferential flap at the top rectangular edge of the flexible liner provides support for the liner, such that the liner does not xe2x80x9cslumpxe2x80x9d into the concrete vault and allow liquid to fill a space between the inner concrete wall and to outer surface of the flexible liner. It is especially important to note that the art in this patent recognizes that some adaptation is important for existing inlet pipes entering the concrete vault at a sidewall. A gasketed set of bolted plates seals the transition of a pipe entering the concrete vessel and passing into the flexible liner. The relatively heavy construction is the result of the impermissibility of leakage from the inside of the liner into the space between the liner and the concrete wall.
U.S. Pat. No. 5,656,766 thus illustrates several advantages and problems of flexible tank liners. Support and sidewall inlet pipe transitions are shown adapted to the special application of that patent, i.e., drainage pits primarily for the petroleum industry. An adaptation combining support and pipe/liner transition is seen in U.S. Pat. No. 4,653,663, wherein a rigid plate supporting the outside surface of the flexible is combined in opposition with an elastomeric plate on the inside surface of that liner.
Although not used to line storage tanks, the flexible liner of U.S. Pat. No. 4,388,357 shows that strips of liner stock can be fabricated on site to form a protective barrier against soil contamination by spilled oil, such as occurs at railroad tank car accidents in remote areas. The bottom of the fabricated flexible liner comprises a fabric screened drain so that the oil can be recovered for commercial use when the oil is withdrawn from the flexible liner. It would be especially useful to adapt flexible tank liner devices so that they could be used in situ, whereby none or relatively little of liquid in an existing storage tank would need to be removed. This is generally not practical in the art of lining tanks with flexible liners, i.e., the liquid is usually leaking into the environment outside of the tank or is further corroding the tank and destroying the support provided by the rigid tank walls.
U.S. Pat. No. 2,807,071 describes, and such description is incorporated herein, a casting apparatus comprising an inner form, a cover plate resting upon the inner form with respect to which file upper edges of the inner form are slidable, and means secured to the cover plate providing for limited upward movement thereof to facilitate separation between the cover plate and a completed-casting, with special application to casket vaults and extendible vaults, such extension being provided by stacking of a second or higher section above the base device described in that patent. The stacked piece is adapted to securingly mate with the piece beneath it, i.e., the cast article of U.S. Pat. No. 2,807,071 when formed comprises an upper inset rim which will accommodate a stacked section above it.
U.S. Pat. No. 3,990,673 describes the apparatus and method for casting concrete septic tanks, burial vaults and the like including an inner form and an outer form. The formation of concrete septic tanks burial vaults and other such structures generally contemplates the casting thereof in a xe2x80x9cformxe2x80x9d. The form usually comprises an inner form and an outer form spaced apart from the inner form and into which the casting material, e.g. concrete, is poured. The outer form is usually a disassembleable rigid structure. The inner form comprises a rigid or expandable and collapsible side walls and end walls. The inner form also includes a top wall or cover plate which mates with the edges of the walls. The method of forming the cast article is basically providing a hollow inner form over which to pour concrete while also providing an outer form to force the concrete to be maintained against the inner form until the concrete hardens and the forms can be removed. The construction of concrete burial vaults is a very time consuming and labor intensive operation. The operation generally consisting of first constructing an inner form having a side wall and. bottom wall configuration identical to the interior surfaces of the side wall and bottom wall of the vault to be formed. The inner form is then mounted a pallet or other flat base surface with the bottom wall of the inner form positioned for upwardly. An outer form consisting of four side walls having a configuration identical to the outer side wall configuration of a vault to be formed was assembled, i.e., typically pivotally hinged at a lower edge of the outer form, around the inner form. The form surfaces in contact with the concrete are next oiled. It is next conventional to suspend a wire mesh, xe2x80x9crebarxe2x80x9d (reinforcing steel rods) or the like into the cavity formed by the inner form and the outer form to provide additional strength to concrete poured into the cavity. The form cavity is next filled with concrete and vibrated to remove voids and to fill the lower sections of the form cavity.
U.S. Pat. Nos. 5,126,095 and 4,934,122 describe a cement
The present invention comprises devices and methods for supplying a flexible liner for septic tanks and for retrofitting existing, leaking septic tanks with such flexible liners.
Metal septic tanks are usually welded along an seam formed from the intersection of an axially symmetrical plane with the cylindrical or rectangular shell. Thus, the weld runs down the side of the septic tank, along the bottom of the tank and up its opposite side. It is an almost universal fault the septic tanks leak along this seam within their xe2x80x9cusefulxe2x80x9d lives, that is, useful in terms of support, not containment. Although in the past such leakage was generally permissible, current regulation, especially among the rural districts of the eastern states of the United States, undigested sewage leaking into the ground immediately next to the septic tank accelerates the rate of corrosion of the tank and unacceptably contaminates the ground water with material having biological oxygen demand that facilities bacterial blooms. The design of septic tanks requires that the sewage remain in the tank for a treatment period so that the BOD and COD is reduced to an acceptable level. Metal septic tank replacement is wasteful since much of the support function of the septic tank is still available, although unacceptable leakage may have occurred.
Some septic tanks have concrete side walls and floors. Liquid sewage containment with concrete makes it certain that crack and fissure propagation via earth shifting and chemical attack will eventually result in unacceptable leakage as for the metal septic tanks. Repair is typically the only reasonable solution, although repair materials are sometimes as hazardous as the leaking sewage. Various patching materials are identified under federal regulations as hazardous if released into the groundwater. The eventual further cracking of the concrete septic tanks mean that both untreated sewage and the patching material may escape later on into the ground water.
One embodiment of the present invention comprises a flexible polymer liner of relatively heavy gauge polyurethane, vinyl, fiber-reinforced polyethylene, ultrahigh molecular weight polyethylene, or the like or layered composites thereof with relatively few rf-welded seams. Preferably, a single, uninterrupted sheet of flexible lining material forms a floor cover, being then sealingly connected to one or more sidewall sheets. The sidewall sheets preferably extend in a single sheet from the top of the septic tank to the floor sheet, thereby having vertical seams. Vertical seams are less subject to separation from the downward pull of gravity than similar horizontal seams. The lining body of the flexible liner thus xe2x80x9ceffectivelyxe2x80x9d seals a polygonal or round vertical in-ground septic tank against leakage. It will be appreciated that absolute prevention of leakage of untreated is preferred but not completely unacceptable. In other tank lining applications with flexible liners, the object of the device is complete sealing of the liquid within the vessel. For septic tanks, some small amount of leakage could be acceptable. Thus, crack propagation in concrete or metal septic tanks means that every leak must be repaired or it will get worse. With the flexible liner of the present invention, a seam leak is unlikely to become larger due to corrosion. A seam leak will likely remain small since little liquid motion is experienced by the flexible liner. Thus, the requirements for fabrication of the lining body and inlet and outlet pipe/liner connections are surprisingly less stringent than those of prior art flexible liners.
Most septic tanks are concrete, although some are currently made with at least fiberglass floors and sidewalls. Patching a leak in a fiberglass septic tank can be challenging. The location of the crack and/or fracture or fiber separation area may be difficult to make sufficiently clean or dry to patch with commonly available materials.
It is heretofore unknown that a retrofit of an existing septic tank could be accomplished for such low cost with a flexible liner. It has been unappreciated that, for design purposes, the septic tank remains full all the time with almost unmeasurable liquid flow movement against the sidewalls or floor. The design requirements are thus dramatically reduced with consideration of that freedom from absolute sealing, turbulence or liquid level changes.
A lining body may be used for sidewall sealing with a relatively rigid or reinforced flexible material and still comprise low cost polymer material. Such support is an alternate embodiment to enhance the ease of initial installation and later drainage.
Another embodiment of the present invention comprises a collar at the top edge of the lining body with flotation means circumferentially and sealingly attached to that top edge. In one form, the lining body flexible material is extended upward, over and around inexpensive flotation material such as styrofoam, thereafter sealing the top edge of the flexible material to an inner or outer surface of the lining body to form a collar pocket. This collar pocket contains sufficient flotation material to keep the upper most surface of the lining body above the liquid (and preferably foam) level in the septic tank. The problem of support of the lining body is thus solved without attachment to the septic tank support (i.e., the concrete or metal shell). With little or no variation in liquid level and little liquid turbulence, the flotation collar pocket material is not subject to abrasion against the inside walls of the septic tank support, thus maintaining an effective air pocket which may alone act as flotation means for the lining body.
It is another embodiment of the present invention to provide inlet and outlet pipe/liner transition taking advantage again of the small change in liquid level and low liquid turbulence. In its simplest form, the lining body may have cut into it an xe2x80x9cXxe2x80x9d or xe2x80x9cYxe2x80x9d opening, whereby the inlet and outlet xe2x80x9cTxe2x80x9d pipes may pass through and be xe2x80x9ceffectivelyxe2x80x9d sealed against unacceptable levels of leakage with a simple metal or plastic band or collar. It is anticipated that this seal would have to withstand no more than about 1-2 psig of pressure with little liquid level change or liquid turbulence. Although the prior art teaches relatively heavy duty devices to accomplish this inlet and outlet pipe/liner transition, those prior art devices are directed to non-quiescent tanks. It is an inventive step to have realized that a much less expensive flexible liner could be made and installed than those of the prior art.
With enabling reference to U.S. Pat. No. 4,388,357, it will be seen that perfect sealing against the environment may not be necessary or economic. Similarly, the present invention also comprises installing a retrofit of one of the embodiments of the flexible liner above into an existing septic tank. Typically, septic tank repair requires complete evacuation and cleaning of the septic tank support structure, i.e., with compressed water spraying and additional evacuation. Cleaning of the septic tank will not be absolutely necessary with installation of the present flexible liner. The corrosion that caused leakage in the original concrete or metal shell rarely affects the structural support of the shell against the earth surrounding it. In fact, sometimes removing the corrosion products from that shell by water spraying may weaken the compressed earth/shell structure so that the shell must be replaced.
In yet another retrofit application, it will be possible to effectively tightly fold and compress the lining body of the flexible liner into a small package which can be submerged into a filled or partially evacuated septic tank. The lining body may be equipped in inflation cuffs, tubes or pockets that, upon inflation by an air pump above ground, will flow the appropriate portions of the lining body into relatively close association with the floor and sidewalls, thereafter moving to the liquid surface the upper edge of the lining body for securing at the top edge of the septic tank shell and adaptation for insertion of the inlet and outlet pipes. The sewage remaining between the flexible liner and the septic tank shell comprises a measurable but acceptable corrosion risk against the structural support shell supporting the flexible liner. Other means of drawing a folded lining body against the appropriate sections of the septic tank shell include using rigid manipulation poles or the like to grasp and position the lining body next to the sidewalls of a full or partially filled septic tank.
In yet another installation method, the flexible liner may be placed on the floor of an evacuated septic tank, the main portion of the flexible liner arranged so that it is loosely arranged about a deflated inflatable and flexible balloon enclosure. This balloon enclosure will have an inflated volume and shape of about the same as or slightly larger than that of the evacuated septic tank. When the balloon enclosure is inflated, the flexible liner is also expanded across the floor and toward the sidewalls of the septic tank. The flexible liner is loosely secured around the balloon enclosure so that the top edge of the flexible liner is forced slowly upward to the top edge of the septic tank sidewall, eliminating manual spreading and lifting in installation of the flexible liner. Loose temporary securing means for the flexible liner about the balloon enclosure comprise elastic straps or ties that can be easily removed as installation aids.
The present invention is applicable to the septic tank type known as xe2x80x9ctightxe2x80x9d tanks, which are not permitted any leaching emission, but must be evacuated periodically to remove accumulated sewage. The sort of evacuation means available in the above cited prior art may be applied to as evacuation means for the present invention.
The lining body of the flexible liner may be enclosed by forming a sealing seam between a top closure piece and the top edge of the lining body. The top closure piece is preferably not gas tight to the environment, since some gas generation is typical of sewage digestion. However, a continuous xe2x80x9czip-locxe2x80x9d or other similar closure for the top closure piece may be used to achieve gas tight closure if such gaseous emissions are a nuisance. A discharge pipe is preferably sealingly attached to the gas-tight top closure piece to conduct away nuisance or hazardous gases for passage through effective cleaning means such as an activated carbon bed or regenerable zeolite bed.
It is a further embodiment of the present invention to provide apparatus and a method for applying a flexible and inexpensive liner to the inside surface of a concrete vault in the concrete casting operation of such a septic tank, casket vault, electrical component containment vault or other concrete vault whereby sufficient liner adhesion and/or attachment to the inside walls of the concrete vault is achieved such that a liquid impermeable seal is provided and the flexible liner will remain effectively attached to the inside wall of the concrete vault during normal usage of the concrete vault. Clearly, the several uses of concrete vaults will instruct the skilled person to choose among the several methods of securing adhesion and/or attachment of the liner described herein. Some of the apparatus and methods described below comprise mainly adhesion of the drying concrete to the smooth or preferably embossed flexible liner while a non-removable liner is obtained with extension of the liner by seam extension or extension attachment into the wet concrete and permitting the concrete to dry about the extension. It is well known that very stiff plastic lugs secured to a stiff plastic base plate will be effectively projected into wet concrete for drying securement therein if sufficient force is maintained to keep the lugs in the wet concrete. It is novel that flexible liner material attached to a flexible base material will be effectively projected into wet concrete for drying securement therein.